Variable displacement engines often employ a valve deactivation assembly including a rolling finger follower that is switchable from an activated mode to a deactivated mode. One method for activating and deactivating the roller finger follower (e.g., a rocker arm) includes utilizing an oil-pressure actuated latch pin disposed within an inner arm of the roller finger follower. In the activated mode, the latch pin engages the inner arm and outer arm together in a latched condition to actuate motion of the outer arm via motion of the inner arm. The outer arm moves a poppet valve to control the intake of gases into the combustion chamber or to exhaust gases from the combustion chamber. In the deactivated mode, the inner arm is disengaged from the outer arm in an unlatched condition, and the motion of the inner arm is not translated to the outer arm and the poppet valve, thereby resulting in a lost motion.
As is typical in the valve deactivator art, mode transitions, either from the latched condition to the unlatched condition, or vice versa, occur only when the roller follower is engaging a base circle portion of the cam. This ensures that the mode change is occurring while the valve deactivator assembly, and more specifically the latching mechanism, is not under a load. Due to the high rotational speed of a cam, it is desirable, but difficult, to reduce the amount of time needed to transition from a latched condition to an unlatched condition in order to execute the transition during a single base circle period. The inventors herein have recognized that one problematic issue that may arise during mode transitions of a rolling finger follower including an oil-pressure actuated latch pin is the presence of air trapped within the latch pin hydraulic circuit. Air trapped within the hydraulic circuit is compressible and increases the amount of time needed to switch from the latched condition to the unlatched condition or vice versa.
The latch pin hydraulic circuit of a switching rolling finger follower may be primed with hydraulic pressure while operating in the latched condition to facilitate the transition to the unlatched condition. In one example, this priming is achieved by utilizing a dual-function hydraulic lash adjuster (HLA) which is configured to provide hydraulic fluid to a latch pin hydraulic circuit at one of a first, lower pressure or a second, higher pressure. The first and second pressures are present at an upper feed port of the hydraulic lash adjuster based on a state of an oil control valve. The hydraulic lash adjuster directs the hydraulic fluid to the latch pin hydraulic circuit via a single port located in a plunger of the lash adjuster. One example approach is shown by Hendriksma et al. in E.P. 1892387. Therein, a dual feed hydraulic lash adjuster is equipped to supply oil to two adjacent oil galleries for valve actuation mechanisms of a cylinder. The two oil galleries are fluidly coupled within the hydraulic lash adjuster in order to provide varying hydraulic fluid pressures to the valve actuating mechanisms dependent on engine conditions. A first gallery flows higher pressure hydraulic fluid to the second gallery in order to carry trapped air in the second oil gallery to a pressure relief valve.
However, the inventors herein have recognized potential issues with such systems. As one example, fluidly coupling a first gallery to a second gallery within a hydraulic lash adjuster may increase a cost and/or complexity of the hydraulic lash adjuster and may result in a greater difficulty of maintenance of the engine oil system.
In one example, the issues described above may be addressed by a system comprising: a first plurality of oil passages, a second plurality of oil passages, and an oil chamber, all disposed within an engine cylinder head; a plug housed within the oil chamber and including a slot fluidly coupled to a first section of the second plurality of oil passages; and a clearance formed between the plug and the oil chamber, the clearance fluidly coupling the first and second pluralities of oil passages. In this way, oil may flow through the clearance from the first plurality of passages to the second plurality of passages.
As one example, each plug may direct engine oil toward separate hydraulic lash adjusters, via the second plurality of passages and a corresponding slot of each plug, with the hydraulic lash adjusters coupled to the second plurality of passages being adjustable between an activated mode and a deactivated mode. The plugs fluidly separate sections of the second plurality of passages in order to enable cylinders of the engine to be individually deactivated. Additionally, oil flowing through the clearance formed by each plug may reduce an amount of air present within the first and second pluralities of passages, thereby reducing a likelihood of airflow into inlets of the hydraulic lash adjusters. Reducing the amount of air within the engine oil system may reduce a likelihood of degradation of the oil system and increase an ease of maintenance of the system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.